In a digitally-controlled printing system, a continuous web of print medium is directed through a series of components. For inkjet printing systems, as the print medium moves through the printing system, liquid, for example, ink, is applied to the print medium using one or more printheads. This is commonly referred to as jetting of the ink.
In commercial inkjet printing systems, the print medium is physically transported through the printing system at a high rate of speed. For example, the print medium can travel 650 to 1000 feet per minute. The printheads in commercial inkjet printing systems typically include multiple jetting modules that jet ink onto the print medium as the print medium is being physically moved through the printing system. A reservoir containing ink or some other material is typically positioned behind each nozzle plate in a printhead. The ink streams through the nozzles in the nozzle plates when the reservoirs are pressurized.
The jetting modules in each printhead in commercial printing systems typically jet only one color. Thus, when different colored inks are used to print color image content there is a generally a printhead for each colored ink. For example, there are four printheads in printing systems using cyan, magenta, yellow and black colored inks. The content is printed by jetting the colored inks sequentially. Each color of ink that is deposited on the print medium is known as a color plane or an image plane. The color planes need to be aligned, or registered with each other, so that the overlapping ink colors produce a quality multi-color image.
Conventionally, at the start of each document, registration corrections are made by shifting the start position of one or more image planes. Additionally adjustments can be made on a document by document basis to adjust the length and width of individual image plane to ensure that the widths and the lengths of the image planes match each other. The shifting of the start position of one or more image planes is an effective means for registering image planes for many documents, where there is an intervening non-printed gap between documents. However there are applications in which it is desirable to print multiple documents consecutively without have a non-print gap between documents. In such applications, a shifting of the start point between documents can lead to a visible artifact at the document seam that is undesirable.
There are several variables that contribute to the registration errors and to stitching errors including physical properties of the print medium, means of conveyance of the print medium, ink application system, ink coverage, and drying of ink. There is a need for improved methods to provide good color-to-color registration for applications in which it is desirable to print multiple documents without a non-print gap between documents.